Recently, genomic structures of various species are being clarified due to technical development in molecular biology, and involvement of gene mutations have been revealed in many genetic diseases and viral diseases. Therefore, establishment of a method for detecting and analyzing a specific gene sequence or a mutant sequence is an important challenge in various fields such as medical science, medical jurisprudence, molecular biology and so on.
Among the gene mutations, attention is focused on single nucleotide polymorphisms (SNPs) since they are recognized as an important means for searching disease-related genes, diagnosis for disease risks, or analysis of drug responses and adverse drug reactions. Therefore, accurate and precise methods for detecting SNPs in a sample nucleic acid are needed.
As methods for detecting and analyzing gene mutations, capillary electrophoresis combined with fluorescence detection and DNA chips are popular. However, these methods have some problems such as a prolonged period of time for analysis.
Molecular tips in STM can directly detect intermolecular electron tunneling between sample and tip molecules, and reveal the tunneling facilitation through chemical interactions that provide overlap of respective electron wave functions, that is, hydrogen-bond, metal-coordination bond, and charge-transfer interactions, respectively (references 1-8). Nucleobase molecular tips were prepared by chemical modification of underlying metal tips with thiol derivatives of adenine, guanine, cytosine, and uracil, and the outmost single nucleobase adsorbate probes intermolecular electron tunneling to or from a sample nucleobase molecule. The inventors found that the electron tunneling between a sample nucleobase and its complementary nucleobase molecular tip was much facilitated compared to its non-complementary counterpart. The complementary nucleobase tip was thereby capable of electrically pinpointing each nucleobase. Chemically selective imaging using molecular tips may be coined “intermolecular tunneling microscopy” as its principle goes, and is of general significance for novel molecular imaging of chemical identities at the membrane and solid surfaces.